On a day of new revelations and disclosures about the National Security Agency's vast, controversial foreign and domestic surveillance programs, the head of the shadowy agency took to the spotlight to defend the programs before a legion of hackers, saying his analysts do not abuse their power "and that's no bulls***."

"What you're hearing is, 'Well they could...,'" NSA Director Gen. Keith Alexander said, referring to claims, most notably by former NSA contractor Edward Snowden, that the agency could read the contents of Americans' communications on a whim. "The fact is, they [NSA analysts] don't. And if they did, our auditing tools would detect them and they would be held accountable, and they know that from the courses they take and the pledge that they made to this nation."

Alexander did not say his agency wasn't capable of collecting the contents of millions of Americans' messages under a program that is designed to collect foreign intelligence, but said technical limitations imposed by the NSA, strict adherance to policy, oversight by other governmental organizations and using a process that is "100 percent" subject to audit and review keeps the analysts from overstepping their bounds. The NSA does collect metadata on communications inside the U.S. as part of a separate program but not the content.

Alexander noted a four-year review of the foreign content collection program, part of which is known as PRISM, by the Senate Select Committee on Intelligence did not find a single "willful violation of the law or the intent of the law in this program."

"We get all these allegations of what they could be doing, but when people check... they find zero times that that's happened," Alexander said. "And that's no bulls***. Those are facts."

A spokesperson for the Senate committee told ABC News Alexander was likely referring to a 2012 Senate Intelligence Committee report on the program that said of the few incidents of non-compliance the committee witnessed over four years, all were the result of human error or technical defect and were promptly reported.

Alexander's salty language was likely a throwback to an earlier, contentious moment in his address when he said the NSA "stands for freedom," only to have an audience member shout, "Bulls***!" and, later, "Read the Constitution!"

Alexander was speaking at the annual Black Hat cyber security conference in Las Vegas, one of the largest gatherings of hackers, industry experts and cyber security professionals in the world.

The relationship between the hackers and federal government has historically been a complicated one -- a balancing act of suspicion from the hackers and a bid by the government to learn the latest from the hairy edge and perhaps recruit some of the best cyber minds around. Though Alexander, the chief symbol of government surveillance, was welcomed at Black Hat, federal officials were politely asked to reconsider attending DEFCON, a similar cyber security conference whose schedule overlaps with Black Hat this year, due to the surveillance program revelations. For the most part, however, the Black Hat audience was welcoming to Alexander and gave him a much larger applause when he took the occasional shot back at the hecklers.

Alexander's speech came the same day columnist Glenn Greenwald at The Guardian published a new report based on secret NSA documents provided by ex-NSA contractor Edward Snowden that detailed a different surveillance program known as XKeyscore -- a program an NSA briefing boasted collects "nearly everything a user does on the internet."

It was also today that James Clapper, the Director of National Security, announced the government would declassify some of the programs made public by Edward Snowden to provide the public a better idea of what the programs are designed to do.

At one point in the speech, Alexander revealed that 20 of the 6,000 NSA cryptologists sent to Iraq and Afghanistan had been killed in action and likened their mission abroad to the analysts' mission at home.

"These are the same people, who take that same oath to uphold and defend the Constitution, are the ones who run these [surveillance] programs," he said.

Alexander Reveals Numbers on NSA vs. Terrorism

During his speech, Alexander also provided new details about the 54 terror-related activities the NSA programs have allegedly helped stop, referring to 42 of them as "plots."

Of the 54 incidents, Alexander said, 13 took place in the U.S., 25 in Europe, five in Africa and 11 in Asia. New leads were provided by an NSA surveillance program in approximately half of those, he claimed.

Similar previous claims by U.S. officials have been called into question, as it was unclear how large of a role the NSA programs actually played. One such claim, made by FBI deputy director Sean Joyce last month, was that the NSA programs helped thwart a plot against the New York Stock Exchange, though court documents reviewed by ABC News showed the plot had fizzled out without the NSA's help.

Before receiving a resounding applause from the audience at the end of his address, Alexander offered a challenge to those who don't like the way the NSA is working now: Help them find a way to do it better.

"This is the greatest gathering of technical talent anywhere in the world," he said. "Maybe you have some ideas of how to do it better."